This invention relates to weatherable polymeric flow and impact modifiers for PVC resin, and to PVC compositions. More particularly, the invention relates to chlorinated hydrogenated high-vinyl polybutadiene and rubbery copolymers thereof, which are useful as modifiers for PVC to impart improved flow, impact, and weathering properties thereto, and to PVC compositions having improved flow, impact and weathering properties.
Polyvinyl chloride (PVC) resins are commonly fabricated from powders or pellets by thermal processes including extrusion and injection molding, during which the particles must be fused into a molten mass. In conventional processing, the fusion and subsequent processing is aided by incorporation of plasticizers. These plasticizers also improve the flow and shear characteristics of the PVC resins by reducing the melt viscosity, thus enhancing the overall processability. Plasticizers, however, are not entirely satisfactory for many purposes inasmuch as they materially reduce the rigidity and heat distortion temperature of the resin when employed in amounts sufficient to improve processability.
Methods for improving impact properties of PVC have included blends of PVC with a second polymeric resin. The second polymeric resin may be a graft copolymer such as for example an ABS or MBS resin. Many polymeric impact modifiers, however, exhibit poor weathering properties, and blends of these with PVC deteriorate rapidly when exposed to ultra violet rays during outdoor use. Impact modifiers having improved weathering characteristics include those prepared by graft-polymerizing methyl methacrylate monomers in the presence of rubbery substrates such as those found in U.S. Pat. No. 3,264,373, and graft copolymers of mixtures of acrylic ester monomers with styrene on rubbery substrates such as those disclosed in U.S. Pat. No. 3,886,232. Although these and related materials exhibit good weathering properties, they require the including of high cost acrylate monomers and are prepared by multi-step polymerization processes which further increase the cost and complexity of their preparation. It is desirable, therefore, to provide alternative, potentially lower cost impact modifiers which can be blended with a PVC resin to improve the impact properties and processability of the resin without materially reducing the weather resistance of the product composition.